With the release of Ubuntu 10.4 on April 29, 2010, an LTS version is now available. While the regular release cycle is six months, Long Term Support for this desktop version is set at three years. You can directly upgrade to Ubuntu 10.04 LTS ("Lucid Lynx") from Ubuntu 9.10 ("Karmic Koala") or from Ubuntu 8.04 LTS ("Hardy Heron"), providing you have all updates and fixes installed.

Available as server and netbook versions as well.
http://www.ubuntu.com/